Capillary bridge rupture in dip-pen nanolithography.

Area of Science:

• Nanotechnology
• Surface Science
• Fluid Dynamics

Background:

• Dip-pen nanolithography (DPN) is a nanoscale printing technique using liquid inks.
• Understanding fluid transfer mechanisms is crucial for controlling DPN resolution and reproducibility.

Purpose of the Study:

• To investigate the role of fluid flows and surface interactions in nanoscale fluid transfer during DPN.
• To elucidate how ink properties and printing parameters influence the amount and pattern of transferred fluid.

Main Methods:

• Systematic variation of ink contact angle, dwell time, and tip retraction speed.
• Analysis of fluid transfer scaling laws with respect to printing parameters.
• Observation of capillary rupture dynamics at the nanoscale.

Main Results:

• Fluid transfer exhibits power-law scaling with dwell time, dependent on the ink's contact angle.
• Tip retraction speed has opposing effects on hydrophilic and hydrophobic surfaces.
• A transition from quasi-static to dynamic capillary rupture was observed at a capillary number of 6 × 10⁻⁶.

Conclusions:

• Nanoscale fluid transfer in DPN is governed by a balance between surface energy and fluid viscosity.
• Retraction speed is a critical parameter for controlling feature size in DPN.
• DPN, optimized with retraction speed control, can achieve polymer feature sizes as small as 14 nm.